The presence of near-zero potential vorticity in the tropical cyclone outflow layer has been documented for many years. Theoretically speaking, the potential vorticity must be close to zero in a state of slantwise moist neutral ascent. Nevertheless, much is not understood about the impact that this low PV layer has upon tropical cyclone development and steady state structure. The purpose of this study is to examine the overall importance of this layer.

The University of Wisconsin-Nonhydrostatic Modeling System (UW-NMS) (Tripoli, 1992) was used to simulate the development of an idealized axi-symmetric tropical cyclone. Sensitivity studies were performed on the idealized tropical cyclone to determine to what extent the storm growth and intensity can be modulated through environmental interactions with the storm outflow. Results of these studies show that environmental resistance against the outflow is strongly reduced because of the low outflow PV. This effectively reduces the storm sensitivity to traditionally hypothesized feedback mechanisms such as radiative transfer in the outflow layer and inertial stability of the environment.